Urban ducks and crows may offer us a connection to nature, but scientists have found that wild birds that live near humans are more likely to harbor bacteria that are resistant to important antibiotics.
Antimicrobial resistance (AMR) is largely caused by the overuse of drugs such as antibiotics among humans and livestock.
The issue is of serious concern: according to data for 2019approximately 4.95 million deaths worldwide were associated with bacterial AMR, including 1.27 million directly caused by such resistance.
Researchers say species of wild birds that tend to turn up in urban environments are reservoirs for bacteria with the characteristics of resistance to a host of drugs.
“What we are basically seeing are genes that confer resistance to antimicrobial agents that will be used to treat human infections,” says Prof Samuel Sheppard, co-author of the research from the Ineos Oxford Institute.
The team says their findings are important as wild birds have the ability to travel considerable distances. Sheppard said a major concern is that these birds could pass on antimicrobial-resistant bacteria to captive birds destined for human consumption — such as those kept on poultry farms.
Write in the journal Current BiologySheppard and colleagues report how they analyzed the genomes of bacteria found in 700 samples of bird droppings from 30 wild bird species in Canada, Finland, Italy, Lithuania, Japan, Sweden, the UK and the US.
The team specifically looked at the presence of different strains of Campylobacter jejuni – a type of bacteria that is ubiquitous in birds as a natural part of their gut microbiome. Such bacteria are a major cause of human gastroenteritis, although antibiotics are generally used only in severe cases.
Sheppard added that each wild bird is generally expected to host a single strain of it C. jejunispecific to that species.
However, the team found that wild birds arriving in urban environments contain many more strains of C. jejuni than those who live away from people.
What’s more, the strains found in urban species contained about three times as many genes known to result in antimicrobial resistance, with these genes also associated with resistance to a broader range of antimicrobials.
The authors suggest that wild birds can pick up antimicrobial-resistant bacteria in a number of ways: gulls and crows, for example, are known to lurk at landfills, while ducks and geese can pick them up in rivers and lakes contaminated with human sewage. .
Dr Thomas Van Boeckel, an expert in antimicrobial resistance at ETH Zurich who was not involved in the work, said the research was unusual as it focused on the impact of antimicrobial use by humans on animals.
“What are the consequences for the birds? We don’t really know, but it seems our people are responsible for this change,” he said.
Dr Danna Gifford from the University of Manchester added the findings could have implications for human health.
“While of concern, the risk of direct transfer of resistance from urban birds to humans is unclear. However, poultry-to-human transmission is well documented,” she said. “With urban development encroaching on agricultural land, increasing contact between urban birds and poultry raises significant concerns about indirect transmission through the food chain.”
Dr Andrew Singer, from the UK Center for Ecology & Hydrology, said more samples were needed to ensure the results held up, but that precautions could be taken.
“The most obvious place to start is to ensure that birds do not congregate in our landfills, wastewater treatment plants and animal manure piles, where both pathogens and AMR abound,” he said. “Furthermore, we must also eliminate the discharge of untreated sewage into our rivers, which exposes all river-using wildlife – and people – to human-associated pathogens and AMR.”
